1. Field of the Invention
The present invention relates to lighting fixtures, and more particularly to means for changing lighting patterns.
2. Description of the Prior Art
In the specialized lighting utilized for surgical procedures, it is frequently desirable to be able to adjust the pattern size of the light pattern on the wound site depending upon the particular procedure being used and/or the progress of the operation during the surgical procedure.
The conventional means of accomplishing a change in focus and/or a change in pattern size is by mechanical movement of the bulb relative to the reflector or reflectors of the optical system. This normally involves utilization of a lever or levers located on the light itself in order to initiate physical lamp source displacement. Fischer et al., U.S. Pat. No. 4,288,844, issued on Sep. 8, 1981 discloses a means for controlling pattern size and/or focus of surgical lighting.
Prior approaches to improving surgical lighting have generally relied on increasing the size of the lighting fixture or the number of light sources. For example, Herold U.S. Pat. No. 3,927,313 discloses a surgical lighting fixture having several individual light sources event arranged around a central axis. A problem with conventional multiple source lightheads however, is that they product multiple shadows when the beams are interrupted.
Single source lightheads eliminate the problem of multiple shadows but do not provide both high intensity and a large pattern of illumination. To achieve the desired intensity, the pattern of illumination must be limited or the wattage of the bulb increased. The achieve a large pattern, the intensity is reduced. Single source surgical lightheads generally offer their best characteristics at a pattern no greater than six inches and an intensity no greater than 6,000 foot candles.
In some applications, for example, cardiovascular surgery, a larger pattern of illumination is preferred. In Europe, the trend is to couple larger surgical lights to provide a larger illumination pattern with a smaller light of greater intensity to pinpoint a critical area.
Where one lighting fixture is used for a variety of applications, those requiring high intensity and those requiring a large pattern, the lighting fixture should be adjustable to accommodate different needs. Several commercially available lighting fixtures provide some adjustability by means of altering the position of the entire lighting fixture relative to the work surface or by means of complicated light source positioning. For example, by altering the distance between the light source and the reflector in the lighting fixture, the pattern size and intensity can be varied.
Gehly et al., U.S. Pat. No. 4,651,257 issued on Mar. 17, 1987 discloses a multiple lighting apparatus designed to reduce shadows while providing a large field of intense illumination. The light rays projected from the reflector converge at an acute angle relative to the axis of symmetry of the lighting apparatus, crossing that axis, to produce a single beam.
Gehly et al., U.S. Pat. No. 4,617,619 issued on Oct. 14, 1986 describes a lighting apparatus having a multiple reflector system which permits the pattern and intensity of illumination to be adjusted by rotation of one of the reflectors.
Several commercially available lighting fixtures include mechanisms for adjusting pattern size. Most of those systems are controlled by persons other than the surgeon or individual working under the light. Many of the conventional systems change the pattern size only at the expense of optical performance. Light intensity and depth of field are often sacrificed.
There is a need for a lighting fixture having a pattern change mechanism which is easily operated by the person using the light. There is a further need for such a pattern change mechanism which will selectively alter the area of light distribution without significantly altering the optical performance of the lighting fixture.